Post your Q here (1 Viewer)

[McLake]

I'm ready and willing to answer ALL question from the chemisrty syllabus ...

[This was a bad idea ....]

 

[BlackJack]

'I have not studied for Chemistry so far AT ALL..., HELP ME! I'M DOOMED!!! MY LIFE ENDS AT 9AM 8/11/2002!!!"

Plz describe/explain/critically analyse/discuss accuracy/justify the entire Chemistry syllabus to me.... (255 marks + one mark for spelling 'chemistry')

btw, if we were to just post our entire correspondence here, wouldn't it make 800 posts faster... just j/k

 

[McLake]

Sorry can't help you BJ ...

(Your beyond the help of lesser mortals such as me)

Anyone else?

 

[doctor]

outline the role of a chemist employed in a named industry and describe thier role in this position

 

[McLake]

Originally posted by doctor
outline the role of a chemist employed in a named industry and describe thier role in this position

OK, for this question you can:

- Use Conquering Chem's answer (v. nice)
- Make it up on the spot (that's my plan)

OR

"Quality Assurance in Food Industry.
Uses AAS to check for trace elements in food, checks that product isn't poisonus. Also determines the amount of 'Na' and other substances found on the ingredients/nutritional information list."

 

[doctor]

thast probably a better idea good work

 

[Raser]

which comes first
the chicken or the egg

 

[McLake]

Originally posted by Raser
which comes first
the chicken or the egg

Sadly outside the scope of the chemisrty syllabus (which I CAREFULLY MENTIONED ...)

My answer however is egg ...

 

[molloby]

From the Cranbrook trial:

21. (b)

Evidence shows that the overal global concentrations of NO2 in the atmosphere has not increased significantly over the last century.

Discuss the human activities that generate localised increases in NO2 concentratons and the chemical processes which prevent localised increases from being dispersed globally.

Explain how these chemical processes pose a further threat to the environment.

Support your answer with relevant chemical equations.

5 marks.

Eeeeep, I have no idea on this one.

 

[Raser]

hey where did you get that smilie??
did you make it urself?

 

[spannar]

From one of the dot points in Acidic Environment

Identify pH sd -log10[H+] and explain that a change in pH of 1 means a ten fold change in [H+]

thx in advance...i am so screwed for chem tmr

 

[McLake]

Originally posted by molloby
Discuss the human activities that generate localised increases in NO2 concentratons and the chemical processes which prevent localised increases from being dispersed globally.

NO2 comes from burning fossil fuels in factoies and cars:

N2 + 2O2 --> 2NO2

UNSURE OF PROCESSES PREVENTING SPREAD, SOMONE PLEASE EXPLAIN THAT.

Explain how these chemical processes pose a further threat to the environment.

NO2 can cause acid rain:

NO2 + H2O --> HNO3 (which I can't balance, hmm ...)

Acid rain destroys plants, kills fish and is genrally bad ...

 

[spice girl]

NO2 is produced from high-temp combustion:

N2 + O2 -> 2NO
nitric oxide reacts with atmospheric oxygen:
2NO + O2 -> 2NO2

This is localised pollution. NO2 causes photochemical smog:
NO2 -uv-> NO + O
O + O2 -> O3

O3 is a radical, irritating the respiratory system, and also can react with hydrocarbon pollutants to produce hydrocarbon radicals.

NO2 won't stay in atmosphere forever: NO2 reacts with water in atmosphere to produce acid rain.
2NO2 + H2O -> HNO2 + HNO3
2HNO2 + O2 -cat.-> 2HNO3

Acid rain is also bad. It damages plants and kills aquatic animals, as well as damages buildings, etc.

 

[superhubert]

help me, i think i'm screwed......
everytime i do a heat of something calculation i fuck it up. why does it change from neutralization to heat of combustion. in the second half of the equation you have to divide by molar mass of some shit and in the other you mulitiply by some number you pluck outa yer ass. could u plz explain??????????????????
to BJ, i'm a hoping chem is as easy as phys...then i might have a hope....

 

[BlackJack]

/\H=mC/\T... (there is a negative, but it's to show that the chemicals have lost energy to heat)

For heat of combustion, this is the total energy that is used up to heat the water.

To get energy (molar heat of combustion) per mole of eg. CH3CH3OH
you'll need to take the change in mass of ethanol and divide it by the molar mass to get the moles of ethanol used.

Finally
molar heat of comb. = /\H / mol. of ethanol...

Heat of neutralisation is only slightly different. The same equation still gives the total amount of energy that is put into the water... this time calculate the total number of moles of the stuff that reacted, if you need to find molar heat of neutralisation.
Look at the equations... eg.
NaOH + HCl -> NaCL + H2O
One mole of each.... so if you put in .5 moles of NaCl and 0.5 moles of HCl, then the total moles that reacted awas 0.5 moles.
molar heat of neutralisation= /\H / 0.5 moles.

 

[superhubert]

ahhh. revelation... i seem to find them alot in chem. cheers!

 

[stuchie]

ok... i have a question

what is the equation for the leclanche cell

each of my textbooks say a different thing so i dunno which one i should learn....

 

[Ozz^E]

Originally posted by molloby

Discuss the human activities that generate localised increases in NO2 concentratons and the chemical processes which prevent localised increases from being dispersed globally.

Human activites..combustion in stationary sources (power stations) and moving ones (vehicles). Basically:

N2 + O2 -> 2NO
2NO + O2 -> 2NO2

these occur at high temps both naturally in lightening and artficially in combustion chambers.

However, when oxides of nitrogen and suldur dioxide for that matter disperse through larger volume sof air, they dissolve in water droplets (rain) and so are washed out of the atmosphere:

for NOX: 2NO2 + H20 -> HNO2 + HNO3

nitrous acid in solution is catalyitically oxidised to nitric acid:

HNO2 + 02 -> 2HNO3

Hence we get ACID RAIN.

NOTE: this is important in assesing the evidence which indictaes increases in atmospheric concentration of Nox and SO2 gases.

 

[Ozz^E]

Originally posted by spannar
From one of the dot points in Acidic Environment

Identify pH sd -log10[H+] and explain that a change in pH of 1 means a ten fold change in [H+]

thx in advance...i am so screwed for chem tmr

identify simply means that u recognise, so:

pH = -log[H3O+] (to base 10)

This scale is NOT linear, it is logarithmic to the base 10 and hence a decrease/increase by one corresponds to a 10 times more acidic/alkaline respectively substance.

 

[doctor]

in a titration which pieces of equipment have to be rinsed with the substance being placed in them and why is this important?